Masterpieces sometimes pop up in the strangest places. Antiques Road Show, that public television stalwart showing unwitting collectors having their finds appraised, has uncovered plenty of surprises, but this is one of the biggest. A Road Show participant from Corpus Christi, Texas, brought Boston-based antiques expert Colleene Fesko a 1904 easel painting by Mexican muralist Diego Rivera.

During the show, which originally aired on January 7, Fesko appraised the piece at $800,000 to $1 million. Depicting a traditionally garbed Mexican peasant posing with a shovel and a basket, the early painting shows a softer, more naturalistic aspect of Diego Rivera’s work than the iconic, abstracted style of the murals he is famous for. Fesko noted that the painting marks a transition point between Rivera’s experiences in the art academy, where he studied since age 10, and his mature career.

The collector who brought the piece in was shocked at the price. “I knew that he was a famous painter but I had no idea what the value would be,” he said. The work had been in his family for over 80 years, after his great grandparents purchased it — a wise investment that the collector protected by keeping the painting in a safe in his office.

Rivera’s portable frescos, made much later in his career, were recently shown at the Museum of Modern Art, and the owner of the 1904 canvas thinks his piece might belong with them: The painting “needs to be in a museum where everyone can look at it,” he said.

In 2008, a Clyfford Still painting brought to the Antiques Road Show was appraised at $500,000, an estimate that may be conservative considering the artist’s auction prices. A group of 18th century Chinese jade vases found in 2009 was valued at $1.07 million, the first item on the show to break the million mark. A one-of-a-kind collection of original artwork from the Peanuts comic by Charles M. Schulz was appraised at $450,000 in 2009. You never know what you might find in your attic!